Commodities

Vegetables: cucurbits

Practices

Crop Production: pollination

Farm Business Management: marketing management

Production Systems: organic agriculture

Summary:

The heart of this project was replicated cucumber, melon and winter squash variety trials at Twin Oaks Seed Farm during the 2014 growing season. The goals were to evaluate resistance to Cucurbit Downy Mildew, to identify resistant seedstocks, and to look at eating quality and productivity in conditions of high downy mildew pressure. Downy mildew became severe in mid August and provided an excellent screen for our trials. We were successful at identifying several downy mildew resistant seedstocks of melon, cucumber and winter squash. Several of these will be very useful to growers as is, and some are useful for future breeding work.

We also conducted a screening for Striped Cucumber Beetle (SCB) preference. 2014 was a relatively low-pressure year for cucumber beetles, but we still managed to obtain useful results and to demonstrate a trial method that has further potential in higher SCB pressure situations.

This project is part of an effort to create and grow a vibrant seed system in our region. As such, we pursued networking and outreach not only about our trial results but about our broader seed movement goals. I presented at several agricultural conferences over the winter of 2014-2015, successfully connecting with growers throughout the mid-Atlantic and Southeast. We also conducted an online grower survey about cucurbit seed needs.

Introduction

Cucurbit Downy Mildew has been the number one limiting factor in cucurbit production at Twin Oaks Seed Farm, affecting seed crops as well as market crops of cucumber, squash, melon, gourd and watermelon every year. Since 2009 downy mildew (DM) has caused severe losses of these crops each year, including several complete crop failures. Downy mildew has a huge economic impact on growers throughout the Eastern U.S.

Cucurbit Downy Mildew is an oomycete pathogen that cannot survive in sub-freezing temperatures. However, it survives the winter in frost-free areas of Florida, Texas and Mexico, and the spores blow north on the wind each year. We have seen DM arrive in Virginia anywhere between June 15th and August 1st.

Mutations in the pathogen since 2004 have rendered most or all formerly-resistant slicing and pickling cucumber varieties non-resistant. (See NC State Study: http://cuke.hort.ncsu.edu/cucurbit/wehner/articles/mscall.pdf). Consequently, most sources of information about downy mildew resistance of melon and cucumber varieties are out-of-date and unreliable. We have found most standard melon, winter squash and cucumber varieties to be downy mildew-susceptible, and unsuited to late-season or mid-season plantings. Even early plantings succumb to the pathogen before the end of harvest some years, or are adversely affected. While organic producers are especially impacted by downy mildew because of a lack of effective fungicide control options, conventional growers are also impacted by the cost of fungicides and fungicide application. Even with fungicide, production can still be seriously affected.

689,100,000 pounds of fresh cucumbers were grown in the top 11 fresh-cucumber-producing states in 2014, worth $168,038,000. 10 of the top 11 states (all but California) are in the eastern US and affected by Downy Mildew. http://usda.mannlib.cornell.edu/usda/current/VegeSumm/VegeSumm-01-29-2015.pdf. 481,740 tons of pickling cucumbers were produced in the US in 2014, worth $175,634,000. All of the top 8 states are Eastern states affected by downy mildew. The majority of cantaloupe melons grown in the US come from the southwestern states. However, Eastern-grown melons, about 10% of the total, are at least a $30,000,000 industry.

In Michigan, which produces roughly 25% of the nation’s cucumbers, cucurbit fungicides cost $6.4 million/year, most of which is used to control downy mildew on cucumbers (Hausbeck et al. 2014: http://cuke.hort.ncsu.edu/cgc/conferences/cuc2014proceedings.pdf ). Extrapolating the cost of fungicides used each year in Michigan to the rest of the Eastern states, farmers spend in the range of $20 million each year on fungicides to manage cucurbit downy mildew. This figure does not include crop losses and reduced yields due to downy mildew.

In this project, we wanted to find varieties of melon, cucumber and winter squash that can withstand downy mildew, to share the results with other growers, and to gather the information necessary to move forward with seed production and breeding work of DMR varieties.

It was also our goal to situate these trials in the context of a broader movement to create a vibrant seed system in our region. Such a movement must include regional trialing, breeding and seed production work, as well as networking and information sharing. We want the results from our trials not only to benefit produce growers, but to provide a model for farmers who participate or who might participate in seed growing, research and breeding in the Southeast and mid-Atlantic. With these goals in mind, I presented results from our trials at several agricultural conferences in the winter of 2014-2015, and conducted a growers survey about cucurbit seed and variety needs.

Project objectives:

1)To perform a replicated trial of 35 cucumber seedstocks, along with an unreplicated screening of 23 additional cucumber seedstocks, in conditions of high downy mildew pressure, in order to identify resistant seedstocks that are able to produce a worthwhile crop in these conditions.

2)To perform a replicated trial of 32 melon seedstocks, along with an unreplicated screening of 4 additional melon seedstocks, in conditions of high downy mildew pressure, in order to identify resistant seedstocks that are able to produce acceptably sweet melons in these conditions (downy mildew impacts melon sweetness).

3)To perform a replicated trial of 20 winter squash / tropical pumpkin seedstocks, along with an unreplicated screening of 23 additional seedstocks, in conditions of high downy mildew pressure, in order to identify resistant seedstocks that are able to grow and yield well in these conditions; also to evaluate eating quality for these seedstocks.

4)To also evaluate the above melon, winter squash and cucumber seedstocks (the replicated entries in the DM trial) for Striped Cucumber Beetle preference.

5)To conduct a grower survey about cucurbit seed and variety needs that can help inform future trialing and breeding work.

6)To reach other growers with our results and ideas on these topics.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.

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